Communication apparatus and communication method

ABSTRACT

A wireless communication apparatus and a wireless communication method wherein even when the permissible delay amount of data is small, the permissible delay thereof can be satisfied. A data type determining part ( 101 ) determines whether the delay of transport data or control information should be allowed or not. A pilot signal insertion control part ( 102 ) decides, based on pilot insertion interval information and allowable delay information, that a pilot signal is placed adjacently to data that is not allowed to delay. A multiplexing part ( 106 ) multiplexes encoded and modulated transport data with the pilot signal generated by a pilot signal generating part ( 105 ) in such a manner that realizes the placement decided by the pilot signal insertion control part ( 102 ).

This is a continuation application of application Ser. No. 13/108,418filed May 16, 2011, which is a continuation application of applicationSer. No. 11/996,576 filed Jan. 23, 2008, which is a national stage ofPCT/JP2006/314901 filed Jul. 27, 2006, which is based on JapaneseApplication No. 2005-220615 filed Jul. 29, 2005, the entire contents ofeach of which are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a wireless communication apparatus anda wireless communication method for changing pilot signal mappingpatterns.

BACKGROUND ART

Radio transmission systems are required to further improve spectrumefficiency and realize high-speed data transmission. The OFDM(Orthogonal Frequency Division Multiplexing) scheme has been consideredas one option of communication schemes meeting these demands.

Further, in radio transmission systems, support needs to be provided forvarious class of QoS (Quality of Service). In particular, support forinteractive services such as game, telephone and video conference mustrealize extremely little communication latency, compared to filetransfer and web browsing services.

Given this background; in systems using the OFDM scheme, considerationon the method of improving throughput is made by reducing the amount ofpilot signals to estimate channel response and increasing the number ofsymbols and subcarriers to which user data is assigned.

For example, Patent Document 1 discloses setting the mapping pattern ofpilot symbols for estimating channel response so as to be responsive tothe variation in channel response according to the time variation andthe frequency variation of the channel. In particular, as shown in FIG.1, for users with respect to whom the time variation of the channel ismoderate, the time interval for mapping pilot signals (the symbolsillustrated with black symbols in the figure) is set wide, and, on theother hand, as shown in FIG. 2, for users with respect to whom thefrequency variation of the channel is moderate, the subcarrier intervalfor mapping pilot signals is set wide (the symbols illustrated withblack symbols in the figure), thereby improving transmission efficiencyin either case. That is, as shown in FIG. 3, the pilot symbol mappingpattern for users with respect to whom the time variation and frequencyvariation of channel response are relatively moderate, is set as shownin FIG. 3.

When receiving processing is performed for the data symbols subject toreceiving processing shown in FIG. 3 (shaded symbols in the figure), thechannel response estimating method on the receiving side requiresperforming interpolation processing in the time domain and the frequencydomain and estimating channel response at time tn, as explained below.

First, channel response estimation values of OFDM symbols between pilotsymbols are calculated in subcarrier fk (k=1, 5, 9). That is, channelresponse estimation values hk (k=1, 5, 9) of subcarriers f1, f5 and f9at time tn are calculated by estimating channel response estimationvalues hk(n−1) and hk(n+1) using pilot signals at time tn−1 and tn+1 andperforming linear interpolation for estimated channel responseestimation values hk(n−1) and hk(n+1).

Next, the channel response estimation values hk(n) (k=2, 4, 6, 8, 10)for the rest of the subcarriers are calculated, by frequency domaininterpolation between channel response estimation values hk(n) (k=3, 7,11) estimated by pilot signals at time tn and channel responseestimation values hk(n) (k=1, 5, 9) estimated by time domaininterpolation.

As described above, interpolation processing in the time domain and thefrequency domain makes it possible to find the channel responseestimation value for each subcarrier at time tn, and data symbolssubject to receiving processing are demodulated using calculated channelresponse estimation values.

Further, in the case of the pilot interval for moderate time variationof channel response shown in FIG. 1, by estimating channel response h(n)and h(n+1) using pilot signals at time tn and tn+1 andlinear-interpolating estimated channel response h(n) and h(n+1), channelestimation values that are responsive to the time variation of channelresponse are found.

Patent Document 1: Japanese Patent Application Laid-Open 2004-530319DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, to perform time domain interpolation processing in theabove-described manner, receiving processing cannot be started unlesschannel response estimation is finished using pilot signals that aremapped after the data symbol subject to receiving processing, whichincreases the processing time for channel estimation and makes itdifficult to realize allowable delay with respect to data that allowslittle delay.

It is therefore an object of the present invention to provide a radiocommunication apparatus and a radio communication method that realizeallowable delay for data that allows little delay.

Means for Solving the Problem

The radio communication apparatus according to the present inventionemploys a configuration having: a pilot signal generating section thatgenerates a pilot signal; a data category determining section thatdetermines whether or not data allows delay, according to the datacategory of transmission data; a pilot insertion control section thatmaps the pilot signal so as to be adjacent to the data determined not toallow delay; a multiplexing section that multiplexes the pilot signalwith the transmission data according to the determined mapping; and atransmitting section that transmits the signal multiplexed by themultiplexing section.

Advantageous Effect of the Invention

According to the present invention, the time required for receivingprocessing is reduced and the roundtrip delay time is reduced, so thatallowable delay can be realized for data that allows little delay.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates how the pilot interval in the time domain iscontrolled with respect to the time variation of channel;

FIG. 2 illustrates how the pilot interval in the frequency domain iscontrolled with respect to the frequency variation of channel;

FIG. 3 illustrates how a channel response estimation value isinterpolated in the time domain and the frequency domain;

FIG. 4 is a block diagram showing a configuration of a radiocommunication apparatus according to Embodiment 1 of the presentinvention;

FIG. 5 is a flowchart showing an operation of a pilot signal insertioncontrol section shown in FIG. 4;

FIG. 6 illustrates OFDM symbol mapping patterns;

FIG. 7 illustrates OFDM symbol mapping patterns;

FIG. 8 illustrates OFDM symbol mapping patterns;

FIG. 9 illustrates OFDM symbol mapping patterns;

FIG. 10 illustrates OFDM symbol mapping patterns;

FIG. 11 illustrates pilot signal mapping patterns in a single carriertransmission scheme;

FIG. 12 is a block diagram showing a configuration of a radiocommunication apparatus according to Embodiment 3 of the presentinvention;

FIG. 13 is a flowchart showing the operation of the pilot signalinsertion control section shown in FIG. 12;

FIG. 14 illustrates a state where pilot symbols are mapped immediatelybefore scheduling information; and

FIG. 15 illustrates a state where the transmission power of pilotsymbols, mapped immediately before scheduling information, is amplified.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below in detailwith reference to the accompanying drawings.

Embodiment 1

FIG. 4 is a block diagram showing the configuration of radiocommunication apparatus 100 according to Embodiment 1 of the presentinvention. First, in the figure, the transmitting side will beexplained.

Data category determining section 101 has a table for determining inadvance whether or not delay is allowed according to the category oftransmission data and the category of control information.

When transmission data or control information is inputted, data categorydetermining section 101 determines whether or not to allow the delay ofinputted signals according to the table and outputs information showingwhether or not to allow the delay (hereinafter “allowable delayinformation”), to pilot signal insertion control section 102.

Pilot signal insertion control section 102 acquires information showingthe interval for inserting pilot signals (hereinafter “pilot insertioninterval information”) from, for example, a control section (not shown),determines the arrangement of pilot signals according to obtained pilotsignal insertion interval information and the allowable delayinformation outputted from data category determining section 101, andoutputs a control signal to multiplexing section 106, so as to controlto map pilot signals in the determined arrangement.

Further, pilot signal insertion control section 102 outputs pilot signalinsertion information for reporting the pilot signal mapping patterns toencoding section 103 before transmission data symbol sequence istransmitted so as to report how pilot signals are mapped. Here, pilotsignal insertion information is transmitted in the header field or othercontrol channels (for example, control channel for reporting scheduleinformation) with modulation parameters (information required fordemodulation such as the modulation scheme and the coding rate) of thetransmission data symbol sequence. Pilot signal insertion controlsection 102 will be described later in detail.

Encoding section 103 performs error correcting coding for thetransmission data, the control information and the pilot signalinsertion information outputted from pilot signal insertion controlsection 102, and outputs encoded data sequence to modulation section104. Modulation section 104 converts the encoded data sequence tomodulation symbols such as QPSK modulation symbols, 16 QAM modulationsymbols and 64 QAM modulation symbols, and outputs the modulationsymbols to multiplexing section 106. Further, pilot signal generatingsection 105 generates pilot symbols and outputs the generated pilotsymbols to multiplexing section 106.

Multiplexing section 106 multiplexes the modulation symbol sequenceoutputted from modulation section 104 with the pilot symbol outputtedfrom pilot signal generating section 105 according to the control signaloutputted from pilot signal insertion control section 102, and outputsthe multiplexed signal to IFFT section 107.

IFFT section 107 converts a frequency domain signal to a time domainsignal by performing IFFT (Inverse Fast Fourier Transform) processingfor the multiplexed signal outputted from multiplexing section 106.

That is, the multiplexed signal is mapped to a plurality of orthogonalsubcarriers. The signal after IFFT processing is outputted to GIattaching section 108.

GI attaching section 108 attaches a GI (Guard Interval) to the signaloutputted from IFFT section 107 and outputs the signal with a GI to RFtransmitting section 109. By attaching a GI, it is possible to reduceISI (Inter Symbol Interference) by delay waves.

RF transmitting section 109 performs transmitting processing such as D/Aconversion and quadrature modulation (up-conversion) for the signaloutputted from GI attaching section 108 and transmits the signal aftertransmitting processing using antenna 110.

Next, the receiving side will be explained. RF receiving section 111performs predetermined receiving processing such as quadrature detection(down-conversion) and A/D conversion on a signal transmitted from thecommunicating party and received by antenna 110, and outputs the signalafter receiving processing to GI removing section 112. GI removingsection 112 removes the GI of the signal outputted from RF receivingsection 111 and outputs the signal after the removal to FFT section 113.FFT section 113 converts the time domain signal to the frequency domainsignal by performing Fast Fourier Transform (FFT) processing for thesignal outputted from GI removing section 112 and outputs the signalafter FFT, to demultiplexing section 114.

Demultiplexing section 114 demultiplexes the signal outputted from FFTsection 113 to pilot symbols and data symbols according to the controlsignal outputted from pilot signal demultiplex control section 118 whichwill be described later, outputs the pilot symbols to channel responseestimating section 115 and outputs the data symbols to demodulationsection 116.

Channel response estimating section 115 recognizes the mapping patternof the pilot symbols outputted from demultiplexing section 114 inadvance, estimates channel response using the pilot symbols based onpilot signal insertion information outputted from decoding section 117,which will be described later, and outputs a channel response estimationvalue to demodulation section 116.

Demodulation section 116 compensates the channel distortion of the datasymbol outputted from demultiplexing section 114 using the channelresponse estimation value outputted from channel response estimatingsection 115, and performs signal point (constellation point) decision byhard decision or soft decision. The signal point decision result isoutputted to decoding section 117.

Decoding section 117 performs error correcting processing for the signalpoint decision result outputted from demodulation section 116 andoutputs received data. Further, decoding section 117 outputs pilotsignal insertion information included in the received data to channelresponse estimating section 115 and pilot signal demultiplex controlsection 118, respectively.

Pilot signal demultiplex control section 118 outputs to demultiplexingsection 114 a control signal for demultiplexing the pilot signal fromthe received data, according to the pilot signal insertion informationoutputted from decoding section 117.

FIG. 5 illustrates the operation of pilot signal insertion controlsection 102 on the transmitting side. Pilot signal insertion controlsection 102 detects pilot insertion tunings according to pilot insertioninterval information and allowable delay information, and startsperforming the processings of step (hereinafter “ST”) 201 and latersteps in FIG. 5. In step ST 201, whether or not data allows delay isdetermined according to the pilot insertion timings and decidedallowable delay information. If the data is determined not to allowdelay (“NO” in ST 201), the flow proceeds to ST 202, and, if the data isdetermined to allow delay (“YES” in ST 201), the flow proceeds to ST203.

Here, data that does not allow delay refers to data where the delay ofreceiving processing influences the round trip time (RTT). That is, ifthe receiving processing delay of data that does not allow delayincreases, the RTT of that data increases. If the receiving processingdelay of data that does not allow delay increases, the RTT of other datathat do not allow delay increases.

In ST 202, the single pilot symbol that enables channel responseestimation alone is determined to be mapped, and a control signalshowing the details of the determination is generated.

In ST 203, a pilot insertion is determined according to pilot insertioninterval information, and a control signal showing the details of thedetermination.

Next, the arrangement of pilot symbols determined by pilot signalinsertion control section 102 will be explained. FIGS. 6 and 7illustrate the arrangement of scheduling information as data that doesnot allow delay (the shaded symbols in the figures), user datacorresponding to the scheduling information (the slash symbols in thefigures), pilot symbols (the symbols illustrated with black symbols inthe figures) and other data symbols (the symbols illustrated with whitesymbols in the figures).

Here, the scheduling information represents control informationtransmitted before corresponding user data is transmitted, includinginformation needed for demodulation of accompanying user data such asterminal ID, modulation scheme, coding rate and a data block size. Todemodulate the following user data, scheduling information needs to bedemodulated before user data. In particular, the control informationrefers to, for example, the shared control channel (HS-SCCH) describedin 3GGP TS 25.212-590.

As shown in FIGS. 6 and 7, pilot signal insertion control section 102determines the arrangement of the pilot signal that enables channelresponse estimation in the OFDM symbol (at time t_(n)) adjacent toscheduling information.

Demodulation processing for scheduling information can be performedusing the channel response estimation value acquired from the pilotsymbol at time tn by mapping the pilot symbol as described above, sothat it is possible to reduce time required for demodulating schedulinginformation.

However, as shown in FIG. 7, when the pilot symbol is mapped afterscheduling information, it is possible to estimate channel response perOFDM symbol to which scheduling information is mapped, by performingtime domain interpolation processing using this pilot symbol and pilotsymbols that have been received earlier (at time_(tn-2) andtime_(tn-1)).

Further, as shown in FIG. 8, pilot signal insertion control section 102may determine the arrangement of pilot signals that enables channelresponse estimation so as to be mapped in OFDM symbols (at time tn)between scheduling information.

Next, the operation of channel response estimating section 115 on thereceiving side shown in FIG. 4 will be explained. First, channelresponse estimating section 115 acquires pilot signal insertioninformation, which has been transmitted from the communicating partyfrom demodulated data to data symbol sequence in advance, and changeschannel response estimation processing based on pilot signal insertioninformation.

As shown in FIG. 3, when pilot signals are mapped sparsely in the timedomain and in the frequency domain, channel response estimating section115 estimates channel response using the mapped pilot signals andperforms frequency domain interpolation processing for the estimatedchannel response estimation value. Further, by performing interpolationprocessing for the channel response estimation value of each subcarriercalculated by time domain interpolation, the channel response estimationvalue is calculated for each frequency and each time. Interpolationprocessing may be started in the time domain or interpolation processingmay be performed in two dimensions for time and frequency.

Further, as shown in FIGS. 6 and 7, if an additional pilot is mapped inthe frequency domain, channel response estimating section 115 estimateschannel response per subcarrier using the pilot symbol at the time atwhich the additional pilot is mapped.

As described above, according to Embodiment 1, by mapping pilot signalsthat enable channel response estimation alone in the OFDM symboladjacent to data that does not allow delay in the time domain, it ispossible to improve the accuracy of channel estimation and reduce theprocessing time required for channel response estimation.

Although a case has been described with the present embodiment wherepilot signals are mapped so as to be adjacent to data that does notallow delay, the amount of pilot signals that enable channel responseestimation alone may be set by replacing part of data signals with pilotsignals.

Further, although a case has been described with the present embodimentwhere pilot signals are mapped to all subcarriers in OFDM symbolsadjacent to data that does not allow delay as shown in FIGS. 6 to 8,pilot signals may be mapped to subcarriers of part of OFDM symbolsadjacent to data that does not allow delay, and user data may be mappedto the rest of the subcarriers as shown in FIG. 9, if the frequencyvariation of channel response is moderate.

Further, although a case has been described with the present embodimentwhere pilot signal insertion information is transmitted in the headerfield of transmission data symbol sequence or other control channels,service category information of transmission data may be reported whenwhether or not there are additional pilots is determined in advanceaccording to the category of transmission data or the category ofcontrol information. In this case, it is possible to determine whetheror not there are additional pilots on the receiving side withouttransmitting pilot signal insertion information.

Further, in the FDMA system in which different subcarriers are assignedto a plurality of communicating parties at the same time, the presentembodiment may be applied to each subcarrier assigned to thecommunicating party.

Embodiment 2

The radio communication apparatus according to Embodiment 2 of thepresent invention has the same components as FIG. 4 of Embodiment 1 andexplanations thereof will be performed with reference to FIG. 4.

As shown in FIG. 10, pilot signal insertion control section 102 mapspilot signals that enable channel response estimation immediately beforescheduling information (at time tn) and immediately after the OFDMsymbol (at time tn′).

By mapping pilot symbols as described above, when the pilot signal isreceived at time tn′, time domain interpolation processing can bestarted for the channel response estimation value acquired from pilotsymbols at time tn′ and time tn, so that it is possible to reduce timerequired for demodulating scheduling information and be responsive tothe time variation of channel response with scheduling information.

Thus, according to Embodiment 2, by mapping pilot signals that enablechannel response estimation alone to OFDM symbols immediately before andimmediately after data that does not allow delay in the time domain, andby performing time domain interpolation processing for channel responseestimation values estimated by the pilot signals, it is possible toreduce time required for channel response estimation and be responsiveto the time variation in channel response of the data that allow littledelay.

Although a case has been described with the present embodiment where theOFDM scheme is used, a single carrier transmission scheme may be used.In this case, additional pilots will be mapped as shown in FIG. 1.

Further, although a case has been described with the present embodimentwhere pilot signals are mapped immediately before scheduling informationas pilot signals adjacent to scheduling information apart from pilotsignals mapped immediately after scheduling information as shown in FIG.6, pilot signals may be mapped between scheduling information as shownin FIG. 8.

Embodiment 3

FIG. 12 is a block diagram showing the configuration of radiocommunication apparatus 300 according to Embodiment 3 of the presentinvention. The same components as FIG. 4 of the present invention areassigned the same reference numerals and detailed explanations thereofwill be omitted. FIG. 12 is different from FIG. 4 in that pilottransmission power control section 302 is further provided and in thatpilot signal insertion control section 102 and channel responseestimating section 115 are replaced with pilot signal insertion controlsection 301 and channel response estimating section 303, respectively.

Pilot signal insertion control section 301 obtains pilot insertioninterval information from, for example, a control section (not shown)and outputs a control signal for controlling to map pilot signals, tomultiplexing section 106, according to the obtained pilot insertioninterval information and allowable delay information outputted from datacategory determining section 101. Further, pilot signal insertioncontrol section 301 outputs a power control signal for controllingtransmission power of a pilot signal to pilot transmission power controlsection 302. Further, pilot signal insertion control section 301 outputsto encoding section 103 pilot signal insertion information for reportinghow pilot signals are multiplexed, reporting whether or not to amplifythe transmission power of pilot signals and reporting the amount ofamplification when the transmission power is amplified. Here, forexample, when whether or not there are additional pilots and whether ornot to amplify transmission power are determined according to thecategory of transmission data and the category of control information inadvance, service category information of transmission data may bereported. In this case, it is possible to determine whether or not thereare additional pilots and an increment of the transmission power ofpilots on the receiving side, without reporting whether or not there areadditional pilots and the increment of the transmission power of pilots.

Pilot transmission power control section 302 amplifies the transmissionpower (amplitude) of the pilot signal outputted from pilot signalgenerating section 105 according to the power control signal outputtedfrom pilot signal insertion control section 301, and outputs theamplified pilot signal to multiplexing section 106.

Channel response estimating section 303 recognizes pilot symbol mappingpatterns outputted from demultiplexing section 114 and whether or not toamplify the transmission power of pilot signals in advance, estimateschannel response using pilot symbols according to pilot signal insertioninformation outputted from decoding section 117, and outputs channelresponse estimation values to demodulation section 116. In this case, ifthe transmission power of the pilot signal is amplified, the level(amplitude) of the channel response estimation value estimated by theamplified pilot signal is adjusted in accordance with the amount ofamplification to the level (amplitude) of the channel responseestimation value estimated by non-amplified pilot signal.

As described above, by amplifying the transmission power of the pilotsignal mapped so as to be adjacent to scheduling information, receivedquality (for example, SNR (Signal to Noise Ratio)) of the amplifiedpilot signal can be improved and the accuracy of channel responseestimation can be improved, so that it is possible to performdemodulation processing for scheduling information without performingaveraging processing for ensuring the accuracy of channel responseestimation.

FIG. 13 illustrates the operation of pilot signal insertion controlsection 301 on the transmitting side. The same components as FIG. 5 areassigned the same reference numerals and detailed explanations thereofwill be omitted. In ST401 in FIG. 13, the transmission power of thepilot symbol determined to be mapped in ST202 is determined to beamplified, and a control signal showing the details of the determinationis generated.

FIG. 14 illustrates a state where pilot symbols are mapped immediatelybefore scheduling information (the shaded symbols in the figure), andFIG. 15 illustrates a state where the transmission power of pilotsymbols, mapped immediately before scheduling information, is amplified.

As described above, according to Embodiment 3, by amplifying thetransmission power of the pilot signal mapped so as to be adjacent todata that dose not allow delay, received quality of this pilot signalcan be improved, so that it is possible to improve the accuracy ofchannel response estimation estimated by this pilot signal.

Although a case has been described above with the present embodimentwhere the transmission power of the pilot signal mapped immediatelybefore scheduling information is amplified as shown in FIG. 6, thetransmission power of the mapped pilot signal may be amplified as shownin FIGS. 7 to 11.

Although a case has been described with the above embodiments wherescheduling information is explained as data that does not allow delay asan example, the present invention is not limited thereto, and controlinformation, where transmission, reception and retransmission of userdata are controlled so as not to perform processing for user datawithout demodulating these information, that is, control informationwhere RTT of corresponding user data is increased may be applicable whentransmitting processing delay, transmission delay and receivingprocessing delay of control information itself increase, such asACK/NACK information and CQI (Channel Quality information or ChannelQuality Indicator). Further, data requiring the real time performance ofcommunication such as audio, video and game, or data that allows lessdelay as a result of repeating retransmission, are also applicable.

Further, although a case has been described with the above embodimentswhere data category determining section 103 determines whether or not toallow delay, the present invention is not limited thereto, and datacategory determining section 101 may determine the degree of allowabledelay in a plurality of steps and may calculate allowable delay inaccordance with data category.

Although a case has been described with the above embodiments as anexample where the present invention is implemented with hardware, thepresent invention can be implemented with software.

Furthermore, each function block employed in the description of each ofthe aforementioned embodiments may typically be implemented as an LSIconstituted by an integrated circuit. These may be individual chips orpartially or totally contained on a single chip. “LSI” is adopted herebut this may also be referred to as “IC”, “system LSI”, “super LSI”, or“ultra LSI” depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSI's, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of an FPGA (FieldProgrammable Gate Array) or a reconfigurable processor where connectionsand settings of circuit cells in an LSI can be reconfigured is alsopossible.

Further, if integrated circuit technology comes out to replace LSI's asa result of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application of biotechnology isalso possible.

The present application is based on Japanese Patent Application No.2005-220615, filed on Jul. 29, 2005, the entire content of which isexpressly incorporated by reference herein.

INDUSTRIAL APPLICABILITY

The radio communication apparatus and the radio communication methodaccording to the present invention has an effect of which allowabledelay can be realized for even data that allow little delay, and areapplicable to, for example, the OFDM radio communication system.

1. A communication apparatus comprising: a receiving unit configured toreceive at least one of a pilot signal for control information and apilot signal for data to a symbol; and a demodulating unit configured todemodulate at least one of the control information and the data usingthe pilot signal, wherein the pilot signal is mapped such that a numberof symbols to which the pilot signal for the control information ismapped are greater than a number of symbols to which the pilot signalfor the data is mapped.
 2. The communication apparatus according toclaim 1, further comprises a channel estimating unit configured toperform a channel estimation using the pilot signal, wherein saiddemodulating unit demodulates at least of the control information andthe data based on the channel estimation.
 3. The communication apparatusaccording to claim 1, wherein the pilot signal is mapped such that anumber of symbols, to which the pilot signal for the control informationis mapped, per a predefined time, are greater than a number of symbols,to which the pilot signal for the data is mapped, per the predefinedtime.
 4. The communication apparatus according to claim 1, wherein thepilot signal is mapped such that the pilot signal for the controlinformation is denser than the pilot signal for the data.
 5. Thecommunication apparatus according to claim 1, wherein the pilot signalfor the control information is mapped to all subcarriers.
 6. Thecommunication apparatus according to claim 1, wherein the pilot signalfor the control information is mapped to a part of all sub carriers. 7.The communication apparatus according to claim 1, wherein the pilotsignal for the control information is mapped close to a symbol, to whichthe control information is mapped.
 8. The communication apparatusaccording to claim 1, wherein the pilot signal for the controlinformation is mapped just after a symbol, to which the controlinformation is mapped.
 9. The communication apparatus according to claim1, wherein the pilot signal for the control information is mapped justbefore a symbol, to which the control information is mapped.
 10. Thecommunication apparatus according to claim 1, wherein the pilot signalfor the control information is mapped between symbols, to which thecontrol information is mapped.
 11. The communication apparatus accordingto claim 1, wherein the control information is an ACK/NACK or a channelquality indicator.
 12. The communication apparatus according to claim 1,wherein the control information is scheduling information.
 13. Thecommunication apparatus according to claim 1, wherein the controlinformation allows little delay.
 14. A communication method comprising:receiving at least one of a pilot signal for control information and apilot signal for data to a symbol; and demodulating at least one of thecontrol information and the data using the pilot signal, wherein thepilot signal is mapped such that a number of symbols to which the pilotsignal for the control information is mapped are greater than a numberof symbols to which the pilot signal for the data is mapped.